However, by the halfway point, the storyline gets caught up in an incoherent tangle from which it can never properly free itself.

After that pacy start, Days of Future Past stumbles, staggers and all but slumps over the finish line.

An exciting prologue staged in the present day sees the Mutants on the brink of extinction at the robotic hands of their dominant enemy, the Sentinels.

In a desperate bid to save the day, Wolverine (Hugh Jackman) is sent back to the 1970s to change the course of history that led to the rise of the Sentinels.

Michael Fassbender in a scene from X-Men: Days of Future Past.Source:Supplied

Wolverine is instructed by Mutant elders Professor Xavier (Patrick Stewart) and Erik Lensherr (aka Magneto, played by Ian McKellen) to enlist the help of their younger selves (James McAvoy and Michael Fassbender) to get the job done.

Further multiplying the imposing odds of Wolverine’s mission is the rogue influence of fellow Mutant Mystique (Jennifer Lawrence). If she goes ahead with the 1973 assassination of a leading genetic scientist (Game of Thrones star Peter Dinklage), then all hope is lost.

The blending of the two eras and two X-Men casts gives Days of Future Past a stop-start rhythm that makes the later stretches of the story very hard to follow.

While there are some astonishing action sequences - such as when Magneto drops a massive football stadium on the White House - there are also some major plot wrinkles that are never satisfactorily ironed out.